1. Field of the Invention
The present invention relates to an optical pickup for optically recording and reproducing information onto and from optical disks.
2. Description of the Prior Art
The structure of a conventional optical pickup will be described with reference to FIG. 20. The optical pickup shown in FIG. 20 has two laser light sources of different wavelengths, that is, a semiconductor laser 101 of a wavelength of 660 nm that performs recording and reproduction onto and from high-density media such as digital versatile disks (DVDs), and a semiconductor laser 115 of a wavelength of 780 nm that performs reproduction from media such as compact disks (CDs).
To an actuator movable member 111 of the optical pickup, two kinds of objective lenses 107 and 118 are attached, and switching between the two kinds of objective lenses is made by the actuator movable member 111 rotating about a rotation shaft 120. The two kinds of objective lenses 107 and 118 are switched between when recording or reproduction onto or from a disk 108 with a base material thickness of 0.6 mm such as a DVD is performed and when reproduction from a disk 109 with a base material thickness of 1.2 mm such as a CD is performed by the different light sources.
First, an optical system that performs recording and reproduction onto and from media such as DVDs will be described. A light beam emitted from the semiconductor laser 101 of high power is converted into a parallel beam by a collimator lens 102, and is incident on a mirror 103. On the mirror 103, a wavelength selective film is formed where light of a wavelength of 660 nm is mostly transmitted and partly reflected and light of a wavelength of 780 nm is substantially totally reflected. Therefore, an extremely small part of the light beam incident on the mirror 103 is reflected and most of the light beam is transmitted. The reflected part of the light beam is directed to a photodetector 110, where the light quantity of the light beam is detected. By doing this, the emission power of the semiconductor laser 101 is monitored to satisfy the function of keeping constant the power on the disk surface in recording and reproduction.
The light transmitted by the mirror 103 is reflected at a reflecting mirror 106, and is transmitted by a polarizing hologram 104 provided on the actuator movable member 111. The polarizing hologram is formed by forming a grating with a depth d on a substrate of an anisotropic material such as lithiumniobate and filling an isotropic material (refractive index n1) in the grooves of the grating. Generally, when the phase difference between light passing through the grooves and light passing between the grooves is xcfx86, the transmittance is represented by cos2("PHgr"/2). When the refractive indices of the substrate for polarized light parallel to the grating grooves and polarized light vertical to the grating grooves are n1 and n2, respectively, for the polarized light parallel to the grating grooves, since xcfx86=0, the transmittance is 1. For the polarized light vertical to the grating grooves, since xcfx86=2xcfx80(n1xe2x88x92n2) d/xcex, by setting the depth d so that xcfx86=xcfx80, the transmittance is 0 and the polarized light is completely diffracted.
Therefore, by considering the polarization direction of the light beam emitted from the semiconductor laser 101 and the bearing of the grooves of the polarizing hologram 104, the light beam from the light source can be transmitted without diffracted when passing through the polarizing hologram 104. The transmitted light is converted from linearly polarized light to circularly polarized light by a quarter wave plate 105, is aperture-limited by an objective lens attachment hole of the actuator movable member 111, is incident on the objective lens 107, and is condensed on the signal surface of the disk 108 with a material thickness of 0.6 mm.
The light beam reflected at the disk 108 passes through the objective lens 107, and is transmitted by the wave plate 105. Since the light beam is converted into linearly polarized light orthogonal to the direction in which the light beam is polarized on the way to the disk 108 at this time, most of the light beam is diffractivey branched by the polarizing hologram 104. These diffracted light beams are reflected at the reflecting mirror 106, are transmitted by the mirror 103, pass through the collimator lens 102, and are condensedly incident on a photodetector 117 integrated with the laser 101. By use of variations in the quantity of this light, a servo signal and an RF signal such as a focus signal or a tracking signal can be obtained.
Next, an optical system that performs reproduction from media such as CDs by use of the other semiconductor laser 115 will be described. A light beam emitted from the semiconductor laser 115 is diffractively branched to xc2x1first order light and to zero order light by passing through a glass hologram 114 not depending on polarization. These light beams are condensed by a collimator lens 113, are reflected at a mirror 112, the mirror 103 and the reflecting mirror 106, are incident on the objective lens 118 provided on the actuator movable member 111, and are condensed as three spots on the signal surface of the disk 109 with a base material thickness of 1.2 mm. The main beam spot is used for an RF signal, and the two sub beam spots, for three beam tracking.
The light beam reflected at the disk 109 passes through the objective lens 108, the reflecting mirror 106, the mirror 103, the mirror 112 and the collimator lens 113, is further diffractively branched by the glass hologram 114, and is condensedly incident on a photodetector 119 integrated with the semiconductor laser 115. By use of variations in the quantity of this light, a servo signal and an RF signal can be obtained.
In optical pickups that perform recording and reproduction of highly dense signal pits such as those on DVDs, it is required to form very small and high-quality light condensation spots on the optical disk surface. Generally, the size of a light condensation spot depends on the numerical aperture (NA) of the objective lens, the light wavelength xcex, and the light intensity at the aperture pupil end of the objective lens, that is, the rim intensity. The light source wavelength xcex and the NA of the objective lens are defined by a specification or the like, for example, for DVDs; xcex is approximately 650 nm, and NA is 0.6. However, to ensure the spot quality commensurate with the numerical aperture, it is necessary to secure a sufficient rim intensity.
Generally, a light beam emitted from a semiconductor laser has an elliptical far field pattern. For this reason, in the optical pickup structure shown as a conventional example, when the rim intensity in the direction of minor axis of the far field pattern is ensured, the rim intensity is considerably high in the direction of the major axis, that is, the amount of eclipse, due to the aperture limitation, of the light beam incident on the objective lens is considerably large in the direction of the major axis.
In an optical pickup for recording, high optical power is required on the disk surface; a power of approximately 12 to 17 mW is necessary as the objective lens exit light quantity. Therefore, it is necessary to cause the optical pickup to operate within the emission power rating of the laser light source by maximizing the transmission efficiency of the optical system. However, in the conventional structure, since the amount of eclipse in the direction of major axis of the emission far field pattern is large, the light quantity loss is large, so that to ensure the power on the disk surface, the margin for the maximum rating is small even though a high-power laser is used.
FIG. 21 is a view showing the structure of another conventional optical pickup for preventing such a light quantity loss. Since the structure of this optical pickup is substantially the same as that of the conventional example of FIG. 20 except for some parts, detailed description thereof is omitted. In the conventional example shown in FIG. 21, a light beam emitted from a high-power semiconductor laser 201 is converted into a substantially parallel beam by a collimator lens 202, and has its diameter increased only in the Y direction of FIG. 21 by being refracted and transmitted by a triangular prism 221, so that the elliptical far field pattern shown by the broken line enlarges in the direction of the minor axis into a circular far field pattern as shown by the solid line. Therefore, by performing such beam shaping, light use efficiency can be increased.
However, in this case, the number of parts of the optical system increases as shown in FIG. 21 and the optical system layout is difficult, so that the size of the optical pickup increases and the number of man-hours of assembly and cost increase.
The far field pattern means the intensity distribution of light on a surface away from the light emission point of a laser light source. Generally, in the case of a semiconductor laser used as a light source for optical disks, the far field pattern is an elliptical intensity distribution such that an emission angle xcex8a in the horizontal direction of the laser chip, that is, in the polarization direction of the emission linearly polarized light and an emission angle xcex8b in a direction orthogonal thereto satisfy the relationship of the following expression (1):
xc2xc less than (xcex8a/xcex8b) less than xc2xdxe2x80x83xe2x80x83(1)
Another problem of the conventional example is aberrations of the optical system. Generally, optical parts constituting an optical system have a certain amount of aberration such as spherical aberration, coma aberration or astigmatism. When such aberration is present, light condensation spots formed by the objective lens are distorted, which significantly affects the recording quality and the reproduction signal quality. Therefore, in manufacturing optical pickups, it is customary to clarify the aberration specifications of the optical elements constituting the optical system and not to use optical elements exceeding a limit.
However, even though a specification is provided to each optical element, the light condensation spot quality cannot be prevented from being degraded by the aberrations of the optical elements accumulating. Particularly, to optical pickups that perform recording and reproduction of highly dense signals, spot distortion is fatal. Moreover, coma aberration and astigmatism significantly affect the margin performance in recording and reproduction because spots are asymmetrically distorted at the time of defocus where the distance between the disk and the best image point increases and decreases.
Coma aberration can be removed when the head is assembled by a tilt adjustment of the objective lens. However, in conventional optical pickups, when astigmatisms of component parts are accumulated, for example, in the same direction, light condensation spots have large astigmatism, so that characteristics for defocus and the like are significantly degraded.
As described above, it is demanded that optical disk apparatuses for recording or reproducing information by use of laser beams be reduced in size, and attempts have been made to reduce optical pickups in size and weight. Typical examples thereof include optical disk apparatuses that records information onto a disk or reproduces information recorded on a disk by use of a semiconductor laser. In these apparatuses, to enhance light use efficiency and obtain light spots having an axisymmetric intensity distribution, it is necessary that the equal intensity line shape of the light beams (hereinafter, abbreviated as the beam shape) be circular.
As described above, since a light beam emitted from a semiconductor laser generally diverges at different angles in directions horizontal and vertical to the p-n junction surface, when the light beam is collimated by use of a collimator lens, the beam shape thereof is elliptical. Therefore, an optical system that converts the elliptical light beam into a circular light beam has previously been proposed.
Or even when it is not highly necessary to enhance light use efficiency and it is unnecessary to shape the elliptical light beam into a circular light beam, there are cases where astigmatism is caused by a laser light source and optical parts and consequently, the quality of the beam spots obtained by the laser light source is degraded. Therefore, a technique has been proposed of making an adjustment to improve the spot quality by generating astigmatism for correction by inserting a beam shaping prism that has a slight beam shaping effect into the optical system and slightly changing the parallelism of the light beam passing through the beam shaping prism.
When conventional optical disks that are set to use wavelengths of 780 nm to 830 nm like CDs although capable of reducing the wavelength of the light source used, improving the optical resolution and increasing the recordable or reproducible frequency band to achieve high density like DVDs is reproduced with a shorter-wavelength semiconductor laser, a sufficient reproduction signal or control signal cannot be obtained because of differences in the reflectance, the absorptance and the like of the recording surface. This problem is noticeable in disks such as CD-Rs standardized as writable CDs and of which reflecting film has a high wavelength dependency.
To solve the above-mentioned two problems, a method has been considered in which two light sources as shown in FIGS. 22 and 23 are used and a beam shaping function is additionally provided.
FIGS. 22 and 23 are views showing the structure of a conventional optical pickup using this method. FIG. 22 shows a case where a high-density optical disk 1044 with abase material thickness of 0.6 mm is reproduced. FIG. 23 shows a case where an optical disk 1050 with a base material thickness of 1.2 mm is reproduced.
In FIG. 22, a light beam 1037 of a wavelength of 650 nm emitted from a semiconductor laser 1060a of a first module 1060 passes through a hologram 1060c, and is converted into an elliptical parallel beam by a condensing lens 1038. The first module 1060 is oriented so that the direction of major axis of the ellipse of the beam pattern coincides with the direction of thickness of the optical disk apparatus. In this figure, since the structure of each optical pickup is two-dimensionally shown, the direction in which the light beam is decentered at a totally reflecting mirror 1041, which direction is actually vertical to the plane of the figure, is rotated 90 degrees about the center of the optical axis on the A plane. This applies to the figures described later.
The elliptical parallel beam is shaped into a circular beam by a beam shaping prism 1039, passes through a compound prism 1040, has its optical path vertically bent at the totally reflecting mirror 1041, passes through aperture limiting means 1042, is condensed by an objective lens 1043, and is applied onto the surface of the optical disk 1044 as a minute light spot 1045. The aperture limiting means 1042 is structured so that light of a wavelength of 650 nm is all transmitted thereby and of light of a wavelength of 780 nm, only an inner part corresponding to a numerical aperture of 0.45 is transmitted thereby. Moreover, the aperture limiting means 1042 is designed so as to be most suitable for a case where the numerical aperture of the objective lens 1043 is 0.6 and the base material thickness of the optical disk 1044 is 0.6 mm. Therefore, the light beam 1037 of a wavelength of 650 nm is converged with a numerical aperture of 0.6.
Then, a light beam 1046 reflected at the optical disk 1044 again passes through the objective lens 1043, has its optical path horizontally bent at the mirror 1041, passes through the compound prism 1040, and is then again incident on the beam shaping prism 1039.
Since the optical path at the beam shaping prism 1039 is reverse in direction to the above-mentioned optical path, the circular reflected beam is reduced in the direction of thickness of the optical pickup into an elliptical beam by the beam shaping prism 1039.
The reflected beam converted into an elliptical beam is converged by the condensing lens 1038, and is incident on the first module 1060. The light beam 1046 incident on the first module 1060 is diffracted at the hologram 1060c, and is incident on a photodetector 1060b to detect a focus control signal for causing the objective lens 1043 to follow the recording surface by use of a so-called SSD (spot size detection) method and a tracking control signal for causing the objective lens 1043 to follow the tracks on the track surface by use of a phase difference method.
Moreover, as shown in FIG. 23, a second module 1047 is provided with a semiconductor laser 1047a of a wavelength of 780 nm. A light beam 1049 of a wavelength of 780 nm emitted from the second module 1047 passes through a hologram 1047c, and is incident on the compound prism 1040. The light beam 1049 slightly diverged by being condensed by a condensing lens 1048 is incident on the compound prism 1040, and is reflected at an optical film 1040a. The light beam 1049 is further reflected at the totally reflecting mirror 1041, and then, only an inner part thereof corresponding to a numerical aperture of 0.45 is transmitted by the aperture limiting means 1042, is incident on the objective lens 1043, and forms a light spot 1051 on the recording surface of the optical disk 1050. By limiting the aperture only in the case of a wavelength of 780 nm, the numerical aperture is 0.45, so that the optical disk 1050 with a base material thickness of 1.2 mm like a CD can be handled.
A light beam 1052 reflected at the optical disk 1050 again passes through the objective lens 1043 and the aperture limiting means 1042, has its optical path horizontally bent at the totally reflecting mirror 1041, and is incident on the compound prism 1040. The incident light beam is mostly reflected at the optical film 1040a, is converged by the condensing lens 1048, and is incident on the second module 1047. The light beam 1052 incident on the second module 1047 is diffracted at the hologram 1047c, and is incident on a photodetector 1047b to detect a focus control signal for causing the objective lens 1043 to follow the recording surface by use of the SSD method and a tracking control signal for causing the objective lens 1043 to follow the tracks on the track surface by use of a push-pull method. While generally, a three beam method is frequently used for the tracking control signal for CDs, in this conventional example, the push-pull method is used for simplification of explanation.
By using the optical system as described above, when the high-density optical disk 1044 designed for a wavelength of 650 nm is reproduced, the semiconductor laser 1060a is turned on, the light beam is brought to a focus on the optical disk 1044, and the reflected light therefrom is received by the photodetector 1060b, whereby the reproduction signal and the control signal can be obtained, and when the optical disk 1050 designed for a wavelength of 780 nm is reproduced, the semiconductor laser 1047a is turned on, the light beam is brought to a focus on the optical disk 1050, and the reflected light therefrom is received by the photodetector 1047b, whereby the reproduction signal and the control signal can be obtained. In this manner, reproduction and recording are performed from and onto the optical disks 1044 and 1050 that are different in thickness and the wavelength for which they are designed.
However, in the above-described prior art, since the beam shaping prism 1039 is inserted between the first module 1060 and the compound prism 1040, the overall optical path length of the optical system is large, so that it is difficult to reduce the optical pickup in size and thickness.
When the beam shaping means is added to the totally reflecting mirror 1041 or the compound prism 1040 for size reduction, since the light beam 1049 emitted from the second module 1047 is not a parallel beam when passing through the beam shaping means, astigmatism is generated, so that an excellent spot cannot be obtained.
An object of the present invention is to provide an optical pickup in which light use efficiency is enhanced without the number of parts increased and light condensing power is ensured.
Another object of the present invention is to realize a structure correcting astigmatism of the optical system.
Yet another object of the present invention is to realize with a simple structure an optical pickup comprising an optical system having two different light sources and NAs.
Still another object of the present invention is to provide an optical pickup, having a plurality of light emission sources, that is small in size and can be manufactured inexpensively, in which a light beam can be converged into an excellent light spot on an optical disk even though a beam shaping function is provided.
One aspect of the present invention is an optical pickup comprising:
a light source that emits a light beam having a far field pattern being elliptical in cross section;
a collimator lens that converts the light beam from said light source into a substantially parallel light beam;
a beam shaping element that performs beam shaping by changing a substantial aspect ratio of the far field pattern of the light beam from said collimator lens;
light condensing means of condensing the light beam shaped by said beam shaping element on an optical information recording medium; and
light detecting means of detecting a light beam reflected at said optical information recording medium.
wherein said beam shaping element makes the cross section of the light beam having been shaped close to a circle by compressing the light beam substantially in a direction of a major axis of the elliptical cross section of the far field pattern, and reflects the light beam from said collimator lens to said light condensing means.
Another aspect of the present invention is an optical pickup wherein said beam shaping element has a light incident and exit surface and a reflecting surface, and the light incident and exit surface and the reflecting surface are nonparallel to each other.
Still another aspect of the present invention is an optical pickup further comprising an adjusting mechanism that corrects an astigmatism in an optical system by changing relative positions of said collimator lens and said beam shaping element.
Yet another aspect of the present invention is an optical pickup wherein said beam shaping element compresses a diameter substantially in the direction of the major axis of the far field pattern within a range of 0.85 to 0.95 with respect to an input light beam.
Still yet another aspect of the present invention is an optical pickup wherein a first light source and a second light source that emit light beams of different wavelengths are provided, and two optical systems comprising said first light source and said second light source share said collimator lens and said beam shaping element.
A further aspect of the present invention is an optical pickup wherein an optical axis of incidence of said collimator lens and an optical axis of incidence on said beam shaping element are different between said two optical systems.
A still further aspect of the present invention is an optical pickup further comprising a light transmitting parallel or nonparallel plate that is disposed between said first light source and said collimator lens and/or between said second light source and said collimator lens.
Further, describing an example of the present invention, a beam shaping element is provided that performs beam shaping in a direction that compresses the light beam in the direction of major axis of the elliptical emission far field pattern of the semiconductor laser. Here, the beam shaping magnification m is defined as the following expression (2):
m=d/Dxe2x80x83xe2x80x83(2)
where D is the beam diameter in the direction of major axis of the far field pattern before the beam is shaped, and d is the beam diameter in the direction of major axis of the far field pattern after the beam is shaped.
Since the light quantity distribution of the beam is gathered inside by compressing the beam in the direction of major axis of the elliptical emission far field pattern, the quantity of the light eclipsed by the aperture limiting member before the beam is incident on the objective lens is reduced, so that light use efficiency can be enhanced. For the effect of reducing the light quantity loss, it is necessary only that the beam shaping magnification be smaller; it is desirable that the beam shaping magnification be at least not more than 0.95. Moreover, a collimator lens is provided that condenses a light beam emitted from a semiconductor laser, the optical path bending and the shaping of the light beam condensed by the collimator lens are performed by the beam shaping element, and an adjusting mechanism is provided that changes the relative positions of the collimator lens and the beam shaping element along the optical axis.
Generally, a spherical wave is generated by changing the relative distance between the light source and the collimator lens, and by the spherical wave passing through the beam shaping element, an astigmatism corresponding to the degree of sphericity of the spherical wave is generated. By adjusting by using this the position of the collimator lens so that an astigmatism reverse to the astigmatism immanent in the optical system is generated, the astigmatism immanent in the optical system can be canceled, so that the quality of light condensation spot by the objective lens can be ensured.
Moreover, when the magnification of the beam shaping by the beam shaping element is 0.85 or higher, the amount of variation in astigmatism with respect to the movement amount of the collimator lens is appropriate, so that realization of adjustment accuracy in the pickup manufacturing process is enabled. Moreover, by the beam shaping magnification being 1 or lower, the intensity at the aperture pupil end in the direction of major axis of the elliptical far field pattern decreases, so that the influence on the light condensing power of the objective lens becomes a problem. However, when the shaping magnification is 0.85 or higher, the deterioration of the light condensing power is only small.
Moreover, in a structure having two optical systems that are different in wavelength and NA, the two optical systems share the collimator lens and the beam shaping element. This is advantageous in size, assembly and cost because an optical pickup having two optical systems can be easily structured while the above-mentioned advantages are obtained. Moreover, since the optical axis of the light beam elevated by the beam shaping element is the same between the two optical systems by the axes of incidence on the collimator lens and on the beam shaping element being different between the two optical systems, one objective lens can be shared by the optical systems and the axis serving as the reference of the tilt adjustment of the objective lens can be made the same between the two optical systems, so that the light condensation spot quality can be ensured for both of the optical systems.
Moreover, in the case of an optical system having two light sources, that is, a first light source and a second light source that are different in wavelength, a light transmitting parallel or nonparallel plate is disposed in a divergent system of the light beam from each of the light sources. This enables the astigmatism generated in each optical system to be independently corrected while the above-mentioned advantages are obtained, so that a high-performance optical pickup can be realized in which the quality of the light condensation spot formed by each of the optical systems is ensured.
A yet further aspect of the present invention is an optical pickup comprising:
a first light source that emits a first light beam;
light condensing means of condensing said first light beam from said first light source;
beam shaping means of shaping said first light beam condensed by said condensing means;
converging means of converging said first light beam shaped by said beam shaping means, on a first optical disk corresponding to said first light beam;
a second light source that emits a second light beam; and
astigmatism providing means of providing a predetermined astigmatism to said second light beam from said second light source,
wherein said second light source is disposed in a position such that the light beam it emits passes through said astigmatism providing means and is directed to said beam shaping means,
said converging means converges said second light beam from said second light source on a second optical disk corresponding to said second light beam,
said astigmatism providing means is disposed between said second light source and said beam shaping means, and
a relationship between a position of said second light source and a position of said astigmatism providing means is such that an astigmatism for reducing an astigmatism generated when said second light beam passes through said beam shaping means is provided to said second light beam having passed through said astigmatism providing means.
A still yet further aspect of the invention shows generic contents of the invention.
An additional aspect of the present invention is an optical pickup comprising:
a first light source that emits a first light beam;
reflecting means of reflecting said first light beam from said first light source, said reflecting means being substantially a plane,
light condensing means of condensing said first light beam reflected at said reflecting means;
beam shaping means of shaping said first light beam condensed by said light condensing means;
converging means of converging said first light beam shaped by said beam shaping means, on a first optical disk corresponding to said first light beam;
a second light source that emits a second light beam; and
astigmatism providing means of providing a predetermined astigmatism to said second light beam from said second light source,
wherein said reflecting means has a function of transmitting said second light beam,
said second light source is disposed in a position such that the light beam it emits passes through said reflecting means and is directed to said light condensing means and said beam shaping means,
said converging means converges said second light beam from said second light source on a second optical disk corresponding to said second light beam,
said astigmatism providing means is disposed between said second light source and said reflecting means, and has a light incident surface and a light exit surface, said light exit surface and said reflecting means being substantially parallel to each other, and
a relationship between a position of said second light source and a position of said light incident surface of said astigmatism providing means with respect to said reflecting means is such that an astigmatism for reducing an astigmatism generated when said second light beam passes through said beam shaping means is provided to said second light beam having passed through said astigmatism providing means.
A still additional aspect of the present invention is an optical pickup wherein said reflecting means and said light exit surface of said astigmatism providing means are in contact with each other, and said reflecting means and said astigmatism providing means are integrated with each other.
A yet additional aspect of the present invention is an optical pickup further comprising an optical element disposed between said second light source and said astigmatism providing means,
wherein a relationship between a position of said second light source and a position of said light incident surface of said astigmatism providing means with respect to said reflecting means is such that an astigmatism for reducing an astigmatism of said second light beam based on said second light source and/or an astigmatism of said second light beam based on said optical element is provided to said second light beam having passed through said astigmatism providing means.
A still yet additional aspect of the present invention is an optical pickup comprising:
a first light source that emits a first light beam;
light condensing means of condensing said first light beam from said first light source;
beam shaping means having a function of shaping said first light beam condensed by said condensing means, and having a reflecting surface that reflects said first light beam;
converging means of converging said first light beam shaped and reflected by said beam shaping means, on a first optical disk corresponding to said first light beam;
a second light source that emits a second light beam; and
astigmatism providing means of providing a predetermined astigmatism to said second light beam from said second light source,
wherein said reflecting surface of said beam shaping means has a function of transmitting said second light beam;
said second light source is disposed in a position such that the light beam it emits passes through said beam shaping means and is directed to said converging means,
said converging means converges said second light beam from said second light source on a second optical disk corresponding to said second light beam,
said astigmatism providing means is disposed between said second light source and said beam shaping means, and has a light incident surface and a light exit surface, said light exit surface and said reflecting surface of said beam shaping means being substantially parallel to each other, and
a relationship between a position of said second light source and a position of said light incident surface of said astigmatism providing means with respect to said reflecting surface of said beam shaping means is such that an astigmatism for reducing an astigmatism generated when said second light beam passes through said beam shaping means is provided to said second light beam having passed through said astigmatism providing means.
A supplementary aspect of the present invention is an optical pickup wherein said reflecting surface of said beam shaping means and said light exit surface of said astigmatism providing means are in contact with each other, and said beam shaping means and said astigmatism providing means are integrated with each other.
A still supplementary aspect of the present invention is an optical pickup further comprising an optical element disposed between said second light source and said astigmatism providing means,
wherein a relationship of a position of said second light source and a position of said light incident surface of said astigmatism providing means with said reflecting surface of said beam shaping means is such that an astigmatism for reducing an astigmatism of said second light beam based on said second light source and/or an astigmatism of said second light beam based on said optical element is provided to said second light beam having passed through said astigmatism providing means.
A yet supplementary aspect of the present invention is an optical pickup comprising:
a first light source that emits a first light beam;
light condensing means of condensing said first light beam from said first light source;
beam shaping means of shaping said first light beam condensed by said condensing means;
converging means of converging said first light beam shaped by said beam shaping means, on a first optical disk corresponding to said first light beam;
a second light source that emits a second light beam; and
reflecting means of reflecting said second light beam from said second light source and transmitting said first light beam, said reflecting means being integrally provided on a predetermined surface of said beam shaping means,
wherein said converging means converges said second light beam from said second light source on a second optical disk corresponding to said second light beam.
A still yet supplementary aspect of the invention shows generic contents of subsequently described 16th and 17th inventions of the invention.
A further aspect of the invention shows generic contents of subsequently described 16th and 17th inventions of the invention.
a first light source that emits a first light beam;
light condensing means of condensing said first light beam from said first light source;
beam shaping means of shaping said first light beam condensed by said condensing means, and transmitting said first light beam;
converging means of converging said first light beam shaped by said beam shaping means and transmitted by said beam shaping means, on a first optical disk corresponding to said first light beam;
a second light source that emits a second light beam; and
reflecting means of reflecting said second light beam from said second light source and transmitting said first light beam, said reflecting means being disposed on a surface of said beam shaping means from which said first light beam exits,
wherein said converging means converges said second light beam from said second light source on a second optical disk corresponding to said second light beam.
Still another aspect of the present invention is an optical pickup comprising:
a first light source that emits a first light beam;
light condensing means of condensing said first light beam from said first light source;
beam shaping means of shaping said first light beam condensed by said condensing means, and reflecting said first light beam;
converging means of converging said first light beam shaped and reflected by said beam shaping means, on a first optical disk corresponding to said first light beam;
a second light source that emits a second light beam; and
reflecting means of reflecting said second light beam from said second light source and transmitting said first light beam, said reflecting means being disposed on a surface of said beam shaping means on and from which said first light beam is incident and exits,
wherein said converging means converges said second light beam from said second light source on a second optical disk corresponding to said second light beam.
Yet another aspect of the present invention is an optical pickup wherein said first light beam emitted from said first light source and said second light beam emitted from said second light source are different in wavelength.
Still yet another aspect of the present invention is an optical pickup wherein said beam shaping means also has a function of correcting chromatic aberration of said first light beam from said first light source.